Home › Lab markers › BUN (Blood Urea Nitrogen)
COMPREHENSIVE METABOLIC PANEL (CMP)
Also printed as: Urea nitrogen · BUN
Educational only — not medical advice.
BUN measures urea nitrogen, a waste product left over when your body breaks down protein. Your liver makes it and your kidneys clear it out. The level reflects both how much protein you are processing and how well your kidneys are filtering.
Because BUN sits at the intersection of hydration, protein intake, and kidney filtering, it is most useful read next to creatinine and eGFR rather than alone. The BUN-to-creatinine ratio often tells your doctor more than either number by itself.
TYPICAL ADULT RANGE
Many labs report roughly 7–20 mg/dL for adults. Ranges vary by lab and shift with age. Reported in mg/dL.
Reference ranges vary by lab, by method, and by age and sex. Always read your own result against the range printed on your report.
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Low BUN is frequently unremarkable. A lower-protein diet, drinking a lot of fluid before the draw, and pregnancy all lower it, and some people simply run low. Liver conditions can also reduce urea production, which is one reason your doctor reads it alongside your liver markers rather than in isolation. If it is new or persistent, mention it at your next visit.
The most common reason for a high BUN is mild dehydration — a hot day, a hard workout, a long stretch without water before the draw. A high-protein diet, a recent course of certain medications, and even a heavy protein meal the night before can nudge it up. Kidney filtering is also part of the picture, which is why your doctor will look at creatinine and eGFR in the same breath. A single elevated BUN with normal kidney markers is a common and usually undramatic combination worth confirming on a repeat draw.
Your doctor is the one who can read this number against your history, symptoms, and medications.
Educational only — not medical advice. Lab results only mean something alongside your history, symptoms, medications, and the rest of your panel. Bring questions to your doctor; they are the one who can interpret your results for you.
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